Category Archives: Renewables

I’ve been interested for a while in getting underfloor heating, probably of the hydronic variety. Underfloor heating offers some benefits in terms of less air movement and noise, and of giving a more liveable ambient heat – there is some evidence that the warmth of your feet is a key determinant of how comfortable your house is in winter.

The concept has been to use a large water storage tank as thermal mass, and to use evacuated tube water heating to heat that tank. This gives most of the benefit of having large thermal mass in your house, whilst giving control over when you take the heat out of that thermal mass.

This blog post explains why I think that’s probably not a great idea anymore, and what I’m thinking instead.

So, I’ve been wondering for a while about whether you can mostly heat your house with a (large) solar hot water system, plus a good sized storage tank to bridge you through cold periods, plus a hydronic (under floor or radiator) system.

I’ve been researching some more today, and probably am not a lot closer to knowing. But what I have learned today I’ll include here, over time I’m going to post some more on this as I form more coherent ideas.

I have a bit of an interest in energy usage. An online book that I read some time ago has just come to my attention again, without the hot air by David MacKay.

This book is interesting as it sidesteps all the discussions about climate change and energy use, and instead takes an engineering viewpoint of the question “could we replace fossil fuel usage with renewables?” The answers are interesting.

One of the things that takes us close to areas that interest me is the use of power in a house. I have been thinking about our next house, which I’m reasonably keen to build in a rural area. That would give us access to a range of alternatives for how we’d build the house, heat the house and power the house. One of the things I’m learning from my reading is that you shouldn’t really try to use one of everything – you end up with lots of small heating or power units that collectively achieve little, and you spend an awful lot of money putting it all together.

So, for example, you can heat with solar passive (windows), wood burners, solar thermal (hot water), heat pumps, gas, electric. It makes little sense to have one of each of these, it makes more sense to have one primary means that is “free” – so solar thermal for example, and one backup mechanism, say a wood burner or a heat pump. Whatever you use has to fit into your overall house plans – so if you’re going off grid with windmills or solar PV, then a heat pump probably isn’t a great idea. If you want cooling as well, or want to take advantage of seasonal storage of heat, then a heat pump may make great sense.

My inclination at the moment is to run underfloor heating using water (hydronic), primary heating coming from an oversized solar hot water system using evacuated tubes, and back that up with either a wood burner/boiler/wetback, or with a heat pump. Excess heat in summer is dumped into a swimming pool and/or into the ground. If a heat pump is in the plans, you can use a ground source heat pump to pull the heat you dumped into the ground in summer back out for heating in winter.

Heat pumps are attractive because they offer cooling, they’re super efficient, they’re very low maintenance, and they offer the opportunity for ground-sourced heat that leverages heat dumped in summer. Wood burners are attractive because they’d use local product (any useful farm should have spare trees to cut down), because the better half likes fire places, and because they work when the power’s off if you go off grid.

It’s not clear to me at the moment that it’d make sense to have both a wood burner and a heat pump, but I’d kind of like to.